GW Pharma’s seizure medicine Epidiolex handily surpassed Wall Street forecasts for sales during the first quarter, and the biotech gave reason for further optimism by announcing Monday that the cannabis-derived drug succeeded in late-stage study aimed at expanding its market.

The Phase 3 trial showed Epidiolex significantly reduced seizure rates in patients with tuberous sclerosis complex, or TSC, compared to placebo. The drugmaker plans to file a supplemental drug application with the Food and Drug Administration in the fourth quarter this year.

From January to March, Epidiolex posted $33.5 million in U.S. net sales, double the market consensus of $16 million. Together, the positive financial and clinical news helped drive GW’s stock up nearly 9% at market open Tuesday.

While $33 million would barely register on the books of many large drugmakers, GW Pharma’s progress in launching Epidiolex (cannabidiol) has given some early proof to the promise of cannabis-based drugs.

“This performance reflects a strong launch, and I believe we have reason to be confident in Epidiolex’s commercial prospects in the short, medium and long term here in the U.S.,” said Julian Gangolli, who recently retired as GW’s U.S. chief commercial officer, on a Monday call with analysts. (Darren Cline has taken over the role.)

GW said more than 7,600 patients have received an Epidiolex prescription since launch, and nearly 2,000 physicians have generated a dispensed prescription.

Some of the sales beat can be explained by a bolus of prescriptions resulting from pent-up demand and initially lengthy timelines to fill prescriptions, Gangolli said. Given this effect, he cautioned against looking at quarter-by-quarter growth going forward, suggesting Epidiolex’s surging sales growth may moderate in future quarters.

GW has made progress on prescription fill times, saying Monday the average time is now down to two weeks. Some of the first commercial patients were waiting more than four weeks when the drug launched last November.

Results from the pivotal Phase 3 study in TSC, meanwhile, could translate to a third FDA-approved indication for Epidiolex. The drug first gained the FDA’s OK last June for two rare forms of epilepsy called Dravet syndrome and Lennox-Gastaut syndrome.

The TSC trial tested Epidiolex at two doses —​ 25 mg/kg and 50 mg/kg —​ and measured seizure rates against placebo. The drug is currently approved at lower dosing levels.

Among the TSC patients in the study, the 25 mg dose actually posted slightly better efficacy than the higher dose, leading to a 49% reduction from baseline in the number of seizures versus the high dose’s 48% lowering. Patients on placebo experienced a 26% reduction.

Investment bank Evercore ISI estimates peak U.S. sales of $1.3 billion for Epidiolex and, in a research note last month, analyst Josch Schimmer argued that figure could be driven higher by approval in additional indications.

Schimmer was one of several analysts that raised their price target following Monday’s earnings, a list that also included analysts from Cowen., Stifel, SVB Leerink and Cantor Fitzgerald.